1. Field of the Invention
The present invention relates to a method of attaching and detaching a preform used to manufacture an optical fiber to and from a support body, and a method of manufacturing an optical fiber using the attaching and detaching method.
Priority is claimed on Japanese Patent Application No. 2010-050779, filed on Mar. 8, 2010, the contents of which are incorporated herein by reference.
2. Description of the Related Art
Plural steps need to be sequentially performed in order to manufacture an optical fiber. Specifically, the manufacturing method includes the steps of (a) manufacturing a silica porous preform by depositing silica glass particles on a target through vapor-phase axial deposition method or outside vapor-phase deposition method, (b) manufacturing a transparent optical fiber preform by performing dehydrating and sintering on the silica porous preform in a sintering furnace, (c) processing a front end portion of the optical fiber preform, (d) measuring a refractive index distribution of the optical fiber preform through a preform analyzer, (e) manufacturing an optical fiber by drawing the optical fiber preform, and the like. In these steps, respective preforms such as the target, the silica porous preform, and the optical fiber preform need to be supported while being hung on a fixed rod-shaped support body.
As a method of attaching and detaching a preform to and from a support body when the preform is supported by the support body, Japanese Unexamined Patent Application, First Publication No. H 11-322357 and Japanese Unexamined Patent Application, First Publication No. 2004-115289 disclose a technique in which penetration holes are respectively provided in an upper end portion of the preform and the support body, and a connection pin is inserted through the penetration holes to connect the preform and the support body to each other. Referring to FIG. 11, the above-described connection method will be described in detail.
First, as shown in Part A of FIG. 11, a preform 2 is moved upward by using a gripper device (not shown), so that an upper end portion 20 is fitted to a concave portion 30 provided in a lower end portion of a support body 3. The upper end portion 20 of the preform 2 is provided with a first penetration hole 20a. The concave portion 30 of the support body 3 is provided with a second penetration hole 30a. At the time of the fitting, the positions of the preform 2 and the support body 3 are aligned with each other so that the penetration holes communicate with each other. Further, in FIG. 11, only the cross-section of the support body 3 is shown.
Subsequently, as shown in Part B of FIG. 11, the rod-shaped connection pin 9 is inserted through the first penetration hole 20a and the second penetration hole 30a. Further, as shown in Part C of FIG. 11, the preform 2 is slightly moved downward by using the gripper device, so that the preform 2 is supported while being hung on the connection pin 9. In general, the connection pin 9 is formed of silica glass.
Subsequently, after a desired process is performed on the preform 2, and as shown in Part D of FIG. 11, the preform 2 is slightly moved upward by using the gripper device. Accordingly, the state in which the preform 2 is hung on the connection pin 9 is released while a downward force is not applied from the preform 2 to the connection pin 9.
Subsequently, as shown in Part E of FIG. 11, the connection pin 9 is taken out from the first penetration hole 20a and the second penetration hole 30a, so that the preform 2 is detached from the support body 3.
Since the known attaching and detaching method is not only simple, but also has a benefit that the preform and the connection pin to be used may be easily processed, the attaching and detaching method is widely used in various manufacturing processes for optical fibers.
In general, the inner diameters of the first penetration hole 20a and the second penetration hole 30a are both set to a size slightly larger than the outer diameter of the connection pin 9. The reason is as follows. When the inner diameter is much larger than the outer diameter of the connection pin 9, a positional deviation may easily occur between the preform 2 and the support body 3 when the preform 2 is supported, and the preform 2 and the support body 3 may be easily damaged due to a decrease in the rigidity thereof. Therefore, when the preform 2 is moved upward as shown in Part D of FIG. 11, the positions of the first penetration hole 20a and the second penetration hole 30a need to be precisely aligned with each other so as to allow taking out of the connection pin 9 from the penetration holes. This is because the connection pin 9 is damaged so that it cannot be used any more when the preform 2 is excessively moved upward. Further, in the worst case, the connection pin 9 is bent, so that the preform is dropped. In order to improve the rigidity of the connection pin 9, there is a proposal to use a connection pin that is foamed of ceramics such as silicon nitride or alumina or metal such as platinum. However, when the connection pin formed of ceramics is used, there is a possibility that impurities are mixed in the preform. Further, in the step of performing dehydrating and sintering on the silica porous preform, the connection pin is exposed to a high-temperature chlorine gas, so that the connection pin is corroded. However, when the connection pin formed of metal is used, the connection pin formed of metal such as platinum which is difficult to be corroded is expensive. For this reason, this is not practical. Therefore, as the connection pin, there is no choice but to use the connection pin formed of silica glass.
For this reason, in the past, such steps in Part D and Part E of FIG. 11 need to be carefully performed on the basis of a worker's experience, where the steps are performed to move the preform 2 upward and to take out the preform. For example, when it is difficult to take out the connection pin 9, the preform 2 may be still hung on the connection pin 9 or foreign material such as fine glass particles may be interposed between the connection pin 9 and the first penetration hole 20a or the second penetration hole 30a although the state in which the preform 2 is hung on the connection pin 9 has been released. Likewise, it is difficult to judge why the connection pin is not able to be taken out from the penetration holes. In this case, it is necessary to repetitively move the preform 2 upward and downward or to attempt to take out the connection pin 9 by a stronger force. The same applies to the case where such operations are automatically performed. Further, in this case, the size of the facility becomes larger. However, even when such operations are performed, eventually damage to the connection pin may no longer be prevented. Likewise, there is a problem in that the damage to the connection pin or the preform may not be completely prevented. Further, the working efficiency is low. Since there are such risks, a problem arises in that a large preform is difficult to be handled.
The invention is made in view of such circumstances, and provides a method capable of simply attaching and detaching a preform to and from a support body without damaging various materials or members in use and also capable of attaching and detaching a large preform.